What do you call a galaxy without stars?
What do you call a galaxy without stars?
Earlier this month, radio astronomers announced that they had discovered the darkest galaxy ever: a cloud of hydrogen gas that resembles our own Milky Way galaxy in many ways, in terms of mass and rotation, but with no stars that anyone can distinguish.
'What we could have here – power – is the discovery of a primordial galaxy, a galaxy so diffuse that it has not been able to easily form stars,” said Karen O'Neil of the Green Bank Observatory in West Virginia. 8 press conference during a meeting of the American Astronomical Society in New Orleans on January 8.
That same week, a group of Spanish astronomers led by Mireia Montes, a research fellow at the Canary Islands Institute of Astrophysics, unveiled the discovery of another nearly starless galaxy that they named Nube, Spanish for “cloud.”
“With our current knowledge, we do not understand how a galaxy with such extreme features could exist,” said Dr. Montes in a statement released by the institute. Dr. Montes is the first author of the new article published in the journal Astronomy & Astrophysics.
And so we can add “dark galaxies” to “dark matter,” “dark energy,” and the other terms of darkness already in the cosmic lexicon.
Dark galaxies are entities whose stars are so sparse and faint that their light cannot be observed other than as a thin, transparent haze that appears to contain no stars at all. (In the beginning, dark galaxies were called “low surface brightness galaxies” or “ultradiffuse galaxies,” but time and jargon march on.) As astronomers with more powerful and smarter eyes continue to look deeper into the sky, galaxies are popping up more and more often , which challenges long-held beliefs about the formation and evolution of galaxies.
The accidental galaxy
These faint ghosts are difficult to find and even harder to study, requiring hours or days of observation to bring their visible starlight into sharp focus. One way is to scan the sky with radio telescopes tuned to the frequency of the interstellar hydrogen gas that permeates galaxies.
Dr. O'Neil was part of one such survey, involving several telescopes, of some 350 galaxies with low surface brightness. “I mistyped the coordinates of the galaxy I wanted to observe, which caused the telescope to point to a different part of the sky than intended,” she said in a recent email. The telescope landed on something she had never seen before.
“It's an all-gas galaxy – it has no visible stars,” she said. “Stars could be be there, we just can't see them.
The galaxy, known as J0613+52, is about 270 million light-years away. It swims amid two billion solar masses of primordial hydrogen produced during the Big Bang, but the galaxy is not forming stars, probably because the gas is too diffuse to clump into the clouds that become stars. Moreover, there are no nearby galaxies with a gravitational influence that could cause such a clump.
“J0613+52 appears to be both undisturbed and underdeveloped,” said Dr. O'Neil. “This could be our first discovery of a nearby galaxy composed of primordial gas.”